In a medium bowl stir together flour, baking powder, cinnamon, baking soda, and salt; set aside. In a large mixing bowl beat together eggs, pumpkin, sugar, and oil. Add the flour mixture; beat until well combined. Stir in chopped pecans, if desired. Spread batter in an ungreased 15x10x1-inch baking pan. Bake in a 350 degree F oven for 25 to 30 minutes or until toothpick inserted in center comes out clean. Cool on wire rack. Frost with Cream Cheese Frosting. Top with pecan halves, if desired. Cut into squares. Store in refrigerator.